New metallic glass material makes robotic gears more graceful

Being able to operate gears at the low temperature of icy moons is a potential game changer for scientists.

For robotics, its all in the movement and gears are essential for precision.

Bulk metallic glass, a metal alloy, doesn’t get brittle in extreme cold. That makes the material perfect for robotics operated in space or on icy planets. Image Credit: NASA/JPL-Caltech

At NASA’s Jet Propulsion Laboratory in Pasadena, California, technologist Douglas Hofmann and his collaborators are building a better gear. Hoffman is exploring how gears made from bulk metallic glass (BMG), a specifically crafted alloy with properties that make it ideal for robotics.

“Our team of researchers and engineers at JPL, in collaboration with groups at Caltech and UC San Diego, have finally put BMGs through the necessary testing to demonstrate their potential benefits for NASA spacecraft,” says Hoffman. “These materials may be able to offer us solutions for mobility in harsh environments, like on Jupiter’s moon Europa.”

This new material is unique because of its metallic structure. Metals have an organized, crystalline arrangement. But if you heat them up into a liquid, they melt and the atoms become randomized. Cool them rapidly enough and you can trap their non-crystalline, “liquid” form in place.

This produces a random arrangement of atoms with an amorphous, or non-crystalline microstructure. That structure gives these materials their common names: “amorphous metals,” or metallic glass.

The material is technically a glass due to its extremely fast cooling. It can flow easily and be blow-molded when heated. When this glassy material is produced in parts greater than about .04 inches (1 millimeter), it’s called “bulk” metallic glass, or BMG.

BMGs have low melting temperatures. That allows parts to be cast using injection-molding technology but with much higher strength and wear-resistance. BMGs also don’t get brittle in extreme cold, a factor which can lead to a gear’s teeth fracturing.

Initial testing has demonstrated strong torque and smooth turning without lubricant, even at -328 degrees Fahrenheit. For robots sent to frozen landscapes, that can be a power-saving advantage.

“Being able to operate gears at the low temperature of icy moons, like Europa, is a potential game changer for scientists,” said R. Peter Dillon, a technologist and program manager in JPL’s Materials Development and Manufacturing Technology Group. “Power no longer needs to be siphoned away from the science instruments for heating gearbox lubricant, which preserves precious battery power.”

The second paper led by Hofmann looked at how BMGs could lower the cost of manufacturing strain wave gears. This type of gear, which includes a metal ring that flexes as the gear spins, is tricky to mass produce and ubiquitous in expensive robots.

Not only can BMGs allow these gears to perform at low temperatures, but they can also be manufactured at a fraction of the cost of their steel versions without sacrificing performance. This is potentially game changing for reducing the cost of robots that use strain wave gears, since they are often their most expensive part.

“Mass producing strain wave gears using BMGs may have a major impact on the consumer robotics market,” Hofmann said. “This is especially true for humanoid robots, where gears in the joints can be very expensive but are required to prevent shaking arms. The performance at low temperatures for JPL spacecraft and rovers seems to be a happy added benefit.”